Generally in the opening-closure system such as the power window of a car, the use of electronic control for implementing an automatic reversal of the action of the window and multiplex communication control constitutes a main current of technology today and as a motor drive system for supplying a current to the motor, a prime mover, as needed and controlling its operation, a motor drive system utilizing relays is generally employed. The typical construction of a conventional motor drive system of this type is as illustrated in FIGS. 7 and 9.
This conventional system is now described.
As shown in FIG. 9, this motor drive system comprises relays 2, 3 for supplying a driving current to a motor 1 to drive it in a normal direction (e.g. the direction of opening the car window) and a reverse direction (e.g. the direction of closing the car window) , respectively, and switches 4, 5 for designating either the normal or the reverse rotation of the motor 1.
Here, the relays 2, 3 comprise exciting coils 2a, 3a (shown in FIG. 7) and contacts 2b, 3b each having a common terminal (C-terminal), a normally open terminal (N.O terminal), and a normally closed terminal (N.C terminal). In the non-energized state where the coils 2a, 3a are not supplied with a current, the C terminal and N.C terminal are interconnected. On the other hand, the C terminal and N.O terminal are interconnected in the energized state where the coils 2a, 3a are supplied with a current.
The N.O terminals of those relays 2, 3 are connected to a power line E1, while the N.C terminals are grounded. The C terminal of the relay 2 is connected to a terminal 1a, one of the two terminals of the winding of motor 1, which is on the side corresponding to the normal rotation of the motor upon connection to the power supply. The C terminal of the relay 3 is connected to a terminal 1b, of said two terminals of the winding of motor 1, which is on the side corresponding to the reverse rotation of the motor on connection to the power supply.
The switches 4, 5 respectively have one contact which is actuated on manipulation by the car driver, for instance, and it is so arranged that when a rotatable common operating means is rotated in one direction, for instance, the switch 4 is turned ON and when said operating means is rotated in the other direction, the switch 5 is turned ON.
Referring to the system illustrated in FIG. 7, the contacts of those switches 4, 5 are disposed in the lines grounding the respective coils 2a, 3a of relays 2, 3 so that the lines are directly opened and closed. There also is the system, as typically illustrated in FIG. 8, in which the contacts of switches 4, 5 are disposed in the lines connecting the respective coils 2a, 3a of relays 2, 3 to the power source so that those lines are opened and closed.
Furthermore, the drive system illustrated in FIG. 7 (or FIG. 8) is provided with transistors 11, 12 (or 11a, 12a) which turn ON/OFF the ground side and power source side, respectively, of the coils 2a, 3a of relays 2, 3 and a processor means 13 (or 13a) which outputs a driving signal for turning one of said transistors ON so as to drive the motor in a given direction according to an external signal or the prevailing circumstances. The processor means 13 (or 13a) may for example be a one-chip microcomputer and, in this case, one terminal each of switches 4, 5 is connected to the input terminal of said processor means so that the opening-closure state (ON-OFF) of switches 4, 5 can be read by said processor means.
In the above motor drive system, one side each of the coils 2a, 3a of relays 2, 3 are directly opened or closed by the contacts of switches 4, 5 to control the action of the motor 1.
Thus, as the switch 4 is operated to close its contact, a current flows to the exciting coil 2a of relay 2 owing to the voltage of the power line E2 to selectively actuate the contact 2b only, with the result that only the terminal la of the motor 1 is connected to the power source E1 through the C terminal and N.O terminal of contact 2b so that the motor is driven in the normal direction.
On the other hand, as the switch 5 is operated and its contact is closed, a current flows to the exciting coil 3a of the relay 3 due to the voltage of the power line E2 to selectively actuate the contact 3b so that only the terminal 1b of the motor 1 is connected to the power source E1 through the C terminal and N.O terminal of the contact 3b, with the result that the motor is driven in the reverse direction.
Furthermore, in the above motor drive system, the control (communication control) function for driving the motor 1 is executed, even in the absence of operation of the switches 4, 5, by the processing function of said processor means 13 (or 13a) according to a motor driving signal inputted externally by, for example, wireless communication. Moreover, the current value of motor 1 during reverse rotation (the rotation in the direction of closing the window) is read by the processor means 13 (or 13a) and if this current value is found to indicate a jam in the window, the processing function of the processor means 13 (or 13a) causes the motor 1 to rotate in the normal direction even in the absence of operation of the switch 4 to thereby operate the window in the opening direction (automatic reversal function).
Thus, when the motor 1 must be driven in the normal direction for executing the above-mentioned communication control or automatic reversal, the processor means 13 (or 13a) outputs only a driving signal for turning the transistor 11 (or 11a) ON. As the transistor 11 (or 11a) is turned ON, a current flows to the coil 2a of relay 2 to actuate the contact 2b regardless of the status of switch 4 so that the motor 1 turns in the normal direction as can be seen from FIGS. 7 and 8.
When it is necessary to rotate the motor 1 in the reverse direction for executing said communication control or the like, the processor means 13 (or 13a) outputs only a driving signal to turn the transistor 12 (or 12a) ON. As the transistor 12 (or 12a) is turned ON, a current flows to the coil 3a of relay 3 to actuate the contact 3b regardless of the status of switch 5 to rotate the motor 1 in the reverse direction.
In the conventional motor drive system described above, when, for example, the car has fallen into the sea or lake and become submerged in water, the phenomenon of a current flowing to the contacts of switches 4, 5 (the so-called leakage) may occur out of occasion depending on the properties of water even if the operating means is not manipulated and, as a consequence, even if the switches 4, 5 are operated, the motor 1 would not turn whether in the normal direction or in the reverse direction.
Thus, when the electrolyte concentration of the water is fairly high, the contacts of switches 4, 5 are interconnected by the electrolytes so that a leak current flows to the coils 2a, 3a and, therefore, depending on the magnitude of the leak current the
First, the system shown in FIG. 5 is basically similar to the drive system described above with reference to FIG. 7 but is characterized in that it includes a switch 21 the contact of which opens and closes in association with the switch 4.
In the illustrated embodiment, the switch 21 comprises a C terminal connected to the power supply terminal of the coil 3a, an N.C terminal connected to the power supply line E2, and an N.O terminal connected to the ground terminal of the coil 3a through a short-circuit line 22. This switch 21 is so constructed that when an operating means is manipulated in one direction for directing the rotation of the motor 1 in the normal direction, its N.O terminal is closed in association with the closing action of the operating switch 4.
Therefore, when the operating means is manipulated in one direction for directing rotation of the motor 1 in the normal direction, the switch 21 is driven in association with the switch 4 in such a manner that the C-terminal and N.O terminal of the switch 21 and the line 22 cause a short-circuit between the power supply terminal and the ground terminal of the coil 3a of the relay 3 for driving the motor 1 in the reverse direction so that those terminals are always brought to the same contacts 2b, 3b of relays 2, 3 are both actuated. As a consequence, the terminals 1a, 1b of the motor 1 are both connected to the power supply side. Once this occurs, even if the switches 4, 5 are operated or the processor means 13 (or 13a) outputs a signal for driving whichever of the transistors, the circuit status shown in FIG. 9 is not altered so that the motor 1 is made inoperable.
It might be contemplated to overcome the above disadvantage by adopting a water-proof structure for the contacts of switches 4, 5 but this is not easily possible from technical points of view. For, since the switches 4, 5 must be such that their contacts be actuated by a mechanical action of a pressing element which has to be exposed within the car interior, it is difficult to mold the contacts and the construction will have to be too complicated in order that the necessary water proofing effect may be achieved.